1. Field of the Invention
This invention relates to the field of robotics. More specifically, the invention comprises a limb articulation system which takes advantage of resonance and mechanical amplification in multi-link leg structures analogous to those found in nature. The invention also features a “dual state” suspension system—again analogous to natural structures—in which the suspension can be switched between a resting/locked state and a moving/free state.
2. Description of the Related Art
Walking robots are in theory capable of traversing irregular terrain and performing many of the functions now performed by human beings. In order to perform similar functions, however, one must typically include multi-link limb systems such as found in natural bipeds and quadrupeds. Such systems have three, four, or more pivoting joints.
The prior art approach has been to provide actuators at each pivoting joint of a multi-link limb system. These actuators apply mechanical force to set a desired angular relationship between the two links that meet at a particular pivoting joint. Sensors at each joint also frequently measure the angular relationship and provide this information to a control system.
Examples of such systems include “Asimo” from Honda (a humanoid biped), “Flame” from Delfts University in the Netherlands (another humanoid biped), and Big Dog, from Boston Dynamics and the Defense Advanced Research Projects Agency (a quadruped). All of these robots are capable of balanced walking at a relatively slow speed. They employ active actuators at each joint in order to directly control the angular relationship between each link in each limb.
The prior art walking robots are incapable of fast speeds. For example, Asimo is capable of only 1.8 mph. Big dog—being a quadruped—can go considerably faster (about 7.4 mph in a trotting gait). However, the prior designs are constrained to walking or trotting gaits which ultimately limit their speed. The speed is constrained by actuator velocity limitation. The prior art contains no velocity amplifying structures, so the actuator velocity limitation is a significant one.
The prior designs do not exploit the natural resonance properties found in animal limbs. It therefore fails to utilize the propulsive motions found in nature. This is true for several reasons. First, the prior designs tend to place relatively heavy actuators near the distal end of the limbs. These add mass which must be swung during the motion of the limbs—thereby limiting the obtainable speed. More importantly, though, the prior art structures simply do not behave like natural limbs in a running gait.
Natural limbs transition through two or more states when an animal changes from walking to running. The operation of the limbs in a running gait is fundamentally different from the operation of the limb in a walking gait. The limbs of a fast animal—such as an ostrich or a horse—undergo significant resonance while the animal is running. The “actuators” (muscles and associated structure), the elastic elements (connective tissues), and the “control system” (the central nervous system) all take advantage of this natural resonance to drive the limb to a high cyclic rate. The result is a motion amplification system that allows the motion of the primary “strong” link (such as the thigh) to be greatly amplified in the portion of the limb which actually contacts the ground.
While the resonance characteristics are most visible in a running gait, they also naturally exist for walking and trotting. In a walk, the resonance in primarily driven by gravity. At higher speeds the resonance is driven by the nonlinear elastics—since when an animal is running its legs are moving much faster than they could move as a pendulum.
Prior art robots do not take advantage of these phenomena, and this is one of the main reasons why prior art robots have been limited in speed. The present invention proposes a robotic limb system which is more closely analogous to the structures found in nature. This novel approach allows a robot constructed according to the present invention to attain much higher speeds. The inventive approach also permits the use of lower energy to achieve the same speed as for the prior art robots.